Method for forming lithium metal anode device stacks with carbon quantum dots

Abstract

A lithium metal anode device stack for energy storage devices and a method for manufacturing the same are provided. In certain embodiments, the anode device stack includes an anode current collector, a first carbon quantum dot layer and a second carbon quantum dot layer disposed on the anode current collector, and a lithium metal layer disposed between the first and second carbon quantum dot layers.

Description

METHOD FOR FORMING LITHIUM METAL ANODE DEVICE STACKS WITH CARBON QUANTUM DOTSBACKGROUNDField

[0001] Embodiments of the present disclosure generally relate to lithium metal containing devices and methods for manufacturing lithium containing devices. More particularly, the disclosure relates to lithium metal anode device stacks for energy storage devices and methods for manufacturing the same.Description of the Related Art

[0002] Rechargeable electrochemical storage systems are currently becoming increasingly essential for many aspects of everyday life. High- capacity electrochemical energy storage devices, such as lithium-ion (Li-ion) batteries, are used in a growing number of applications, including portable electronics, medical, transportation, grid-connected large energy storage, renewable energy storage, and uninterruptible power supply (UPS). In each of these applications, smaller battery sizes are crucial for continued innovation. Li-ion batteries typically include an anode electrode, a cathode electrode, and a separator positioned between the anode electrode and the cathode electrode. Due to their high energy density, Li-ion batteries have high potential as smaller batteries, but can present difficulties in the manufacturing process due to the lithium of the lithium metal anode layer.

[0003] Lithium is an alkali metal and like the heavy element homologs of the first periodic table group, lithium is characterized by a strong reactivity with a variety of substances. Lithium reacts violently with water, alcohols and other substances that contain protic hydrogen, often resulting in ignition. Lithium is also unstable in air and reacts with oxygen, nitrogen and carbon dioxide. As such, due to its strong reactivity properties, lithium is normally handled under an inert gas atmosphere (noble gases such as argon). As a result, lithium provides several challenges when it comes to processing, storage, and transportation.

[0004] Current methods for building lithium metal anodes for Li-ion batteries includes using passivation layers, such as a lithium carbonate passivation layer to protect the thin lithium film layer from oxidation and damage, as well as prevent unwanted reactions. However, such passivation layers generally have a thickness ranging from about 100 nm to about 200 nm which increases layer resistance and can lead to faster capacitance decay.

[0005] Therefore, there is a need for improved lithium metal anode device stacks for improving the quality, safety, and electrochemical performance of Li-ion batteries.SUMMARY

[0006] Embodiments described herein generally relate to metal electrodes for energy storage devices, more specifically, lithium metal anode device stacks and methods for fabricating the same.

[0007] In one embodiment, a method for forming a device stack is provided. The method includes forming a first carbon quantum dot layer over a release layer disposed over a flexible support layer, and depositing a lithium metal layer on the first carbon quantum dot layer. The method also includes forming a second carbon quantum dot layer over the lithium metal layer, and transferring the release layer, the first carbon quantum dot layer, the lithium metal layer, and the second carbon quantum dot layer to a receiving substrate. The receiving substrate includes a current collector. In other embodiments, the receiving substrate includes an anode layer disposed on a current collector or a separator.

[0008] In another embodiment, a lithium metal anode device stack is provided. The device stack includes an anode current collector, a first carbon quantum dot layer and a second carbon quantum dot layer disposed on the anode current collector, and a lithium metal layer disposed between the first and second carbon quantum dot layers.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this disclosure and are therefore not to be considered limiting of its scope, for the disclosure may admit to other equally effective embodiments.

[0010] FIG. 1 illustrates a flow chart of a method of forming an exemplary lithium metal anode device stack, according to certain embodiments herein; and

[0011] FIGs. 2A - 2G illustrate the various operations of the method of FIG. 1 , according to certain embodiments herein.

[0012] To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.DETAILED DESCRIPTION

[0013] Embodiments of the present disclosure described herein generally relate to metal electrodes, more specifically lithium metal anode device stacks and methods for fabricating the same.

[0014] Thin film lithium metal layers play a vital role in the development of Li-ion batteries. The thin film lithium metal layer is used in making lithium metal anode device stacks for the Li-ion battery. The thin film lithium metal layer may also be implemented as a pre-lithiation layer to protect the anode of the Li-ion battery during the first cycle charge. Since lithium is highly reactive, special conditions such as an inert gas atmosphere is needed when handling and transferring such lithium metal layers during fabrication of thelithium metal anode device stacks. When lithium is not kept in a high vacuum or an inert atmosphere, it quickly reacts creating undesirable compounds, e.g. L2O & LisN. These reactions can severely degrade battery performance.

[0015] Various layers and barriers can be used to protect the thin film lithium metal layer. Protective surface treatments have been developed for lithium metal. One method of protective surface treatment of lithium metal consists of coating the lithium metal or thin film lithium metal layer with a wax layer, for example, polyethylene wax. However, a large amount of coating agent is generally applied and can interfere with subsequent processing of the thin film lithium metal layer. As mentioned above, lithium carbonate passivation layers can also be used to protect the thin film lithium metal layer. However, the thickness required for such layers can also lead to faster degradation in battery performance.

[0016] Aspects of the present disclosure provide techniques for more effectively protecting thin film lithium metal layers implemented in lithium metal anode device stacks of Li-ion batteries or as used in pre-lithiation implementations. As discussed below in further detail, the techniques described herein provide a method for using carbon quantum dots (CQDs) in the fabrication of lithium metal anodes. Embodiments of the methods described herein are applicable to lithium-ion batteries using solid electrolytes (e.g., solid-state batteries) as well as lithium-ion batteries, which use liquid or polymer electrolytes. In some embodiments, the CQDs may be used to protect thin film lithium metal layers from moisture and oxidation. As applied to Li-ion batteries, the CQDs can improve the stability and conductivity of the lithium metal layer, the electrochemical performance of the Li-ion battery, and the overall safety of the Li-ion battery fabrication process. Not to be bound by theory, but it is believed that the CQDs can decrease the resistance and impedance around the anode, thereby improving the cycle life of the battery.

[0017] CQDs are zero-dimensional carbon-based nanomaterials known for their small size and relatively strong fluorescence characteristics. CQDs can have sizes ranging between about 1 nm and about 100 nm with someform of surface passivation. CQDs can have abundant functional groups on the surface which could facilitate the preparation of multi-component electrical active catalysts. CQDs have a number of properties that make them ideal for use in Li-ion batteries, including superconductivity, rapid electron transfer, large, exposed surface area, and chemical inertness. CQDs can also be prepared simply and inexpensively by multiple techniques, such as the arc-discharge method, microwave pyrolysis, hydrothermal method, and electrochemical synthesis.

[0018] Lithium metal anodes may be manufactured by transferring one or more layers including an alkali metal layer, for example, a lithium containing layer or a thin film lithium metal layer, to a current collector, for example, a copper current collector. Substrate independent direct transfer (SIDT) is a method for forming lithium metal anode device stacks by transferring the alkali metal layer (e.g., the lithium metal layer or thin film lithium metal layer) to a current collector in embodiments where the lithium metal layer functions as a lithium metal anode layer, or for pre-lithiating an anode material layer already formed on the current collector.

[0019] FIG. 1 illustrates a flow chart of a method 100 for forming a lithium metal anode device stack. FIGs. 2A-2G illustrates cross-sectional views of an energy storage device structure 200 during the various operations of the method 100. Although FIGs. 2A-2G are described in relation to the method 100, it will be appreciated that the structures disclosed in FIGs. 2A-2G are not limited to the method 100, but instead may stand alone as structures independent of the method 100. Similarly, although the method 100 is described in relation to FIGs. 2A-2G, it will be appreciated that the method 100 is not limited to the structures disclosed in FIGs. 2A-2G but instead may stand alone independent of the structures disclosed in FIGs. 2A-2G. It should be understood that FIGs. 2A-2G illustrate only partial schematic views of the energy storage device structure 200, and the energy storage device structure 200 may contain any number of additional layer and / or additional materials common to energy storage devices, which are not shown for the sake of brevity. It should also be noted that although the method 100illustrated in FIG. 1 is described sequentially, other process sequences that include one or more operations that have been omitted and / or added, and / or have been rearranged in another desirable order, fall within the scope of the implementations of the disclosure provided herein.

[0020] It should also be noted that although the method 100 illustrated in FIG. 1 is described sequentially, other process sequences that include one or more operations that have been omitted and / or added, and / or have been rearranged in another desirable order, fall within the scope of the embodiments of the disclosure provided herein.

[0021] Referring to FIG. 2A, at operation 110 a flexible support layer 210 is provided. The flexible support layer 210 has a front side 21 OF (also referred to as a front surface) and a backside 210B (also referred to as a back surface) opposite the front side 21 OF. The flexible support layer 210 may comprise any suitable material that is compatible with the targeted processing conditions. In some embodiments, the flexible support layer includes a plurality of sub-layers. In one or more embodiments, which can be combined with other embodiments, the flexible support layer 210 can be or include, one or more layers selected from plastic, polymer materials, metallized plastic, metals, paper, multilayers thereof, or a combination thereof Example of suitable polymer materials include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyimide (PI), poly(methyl methacrylate) (PMMA), cellulose tri-acetate (TAC), polypropylene (PP), polyethylene (PE), polycarbonates (PC), bio degradable polymer such as Polyethylene 2,5-furandicarboxylate (PEF), multilayers thereof, or a combination thereof. In one or more embodiments, which can be combined with other embodiments described herein, the flexible support layer 210 is a web-based substrate.

[0022] In one or more embodiments, which can be combined with other embodiments described herein, the flexible support layer 210 has a thickness in a range from about 1 micron to about 100 microns, such as in a range from about 10 microns to about 50 microns, or in a range from about 25 microns to about 50 microns.

[0023] Referring to FIG. 2B, at operation 120 a release layer 220 is formed on the front side 21 OF of the flexible support layer 210. In one or more embodiments, which may be combined with other embodiments, the release layer 220 and the flexible support layer 210 are pre-fabricated. The release layer 220 has a front side 220F (also referred to as a front surface) and a backside 220B (also referred to as a back surface) opposite the front side 220F. In one or more embodiments, the release layer 220 is deposited on the front side 21 OF of the flexible support layer 210 such that the backside 220B of the release layer 220 contacts the front side 21 OF of the flexible support layer 210. Any suitable process may be used to form the release layer 220 on the front side of the flexible support layer 210. The release layer 220 may be deposited using non-vacuum coating techniques, for example, coating techniques performed in the atmosphere.

[0024] The release layer 220 may be or include any material suitable for releasing the anode device stack during the SIDT process. The release layer 220 may be or include polymer release layers (for example, plastics, silicone, polymethylacrylate (PMA), polyethylene terephthalate (PET), fluorocarbons, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), etc.), poly(olefin sulfones), organic materials, inorganic materials, among other materials. In some embodiments, which can be combined with other embodiments, the release layer 220 includes one or more nanosheets, such as one or more two-dimensional (2D) materials. In one or more embodiments, which can be combined with other embodiments, the release layer has a thickness of about 1 nm to about 500 nm, such as about 10 nm to about 300 nm, such as about 50 to about 200 nm. In some embodiments, the release layer includes a plurality of sub-layers, each layer having a thickness of about 5 nm or less.

[0025] Organic or polymer based release layers can be deposited using wet-chemistry coating processes, for example, slot die coating techniques, comma bar coating techniques, or gravure coating techniques, or vacuum deposition techniques as described.

[0026] The release layer 220 may be or include inorganic materials, for example, BN, AIOx, AIOOH, Al, or a combination thereof. In some embodiments, the release layer 220 includes a multi-layer structure, for example, a multilayer structure of AI / AIOx / AIOOH. Inorganic based release layers can be deposited using vapor deposition techniques, for example, PVD techniques such as sputter deposition and electron beam deposition techniques.

[0027] In one or more embodiments, the polymer material of the release layer 220 is selected so that the SIDT stack can be debonded from flexible support layer 210 by photo-initiated lift-off, for example, a laser lift-off process, wherein the polymer material interacts with photons entering from the flexible support layer 210.

[0028] In one or more embodiments, the release layer 220 can be or include a polymer material that is capable of photoinduced depolymerization. In one or more embodiments, the polymer material can be or include a poly(olefin sulfone) material capable of photoinduced depolymerization. The poly(olefin sulfone) may be combined with photo base generators (PBGs). The poly(olefin sulfone) can be doped with a photosensitizer, for example, pyridine N-oxide. The depolymerization process can be induced by, for example, X-rays, electron-beam irradiation, or low-energy irradiation. Suitable poly(olefin sulfone) materials include poly(1 -butene sulfone) (PBS), poly( 1 -pentane sulfone) (PPS), poly( 1 -hexane sulfone) (PHS), poly( 1 -octene sulfone) (POS), poly(cyclopentene sulfone), poly(2-methyl-1 -butene sulfone) (PMBS), poly(2-methyl-1 -pentene sulfone) (PMPS), poly(2-methyl 1 -hexene sulfone) (PMHS), poly(2-methyl-1 -nonene sulfone) (PMNS), poly(cyclohexene sulfone), or a combination thereof.

[0029] Referring to FIG. 2C, at operation 130, a first carbon quantum dot (CQD) layer 230 is formed over the release layer 220. The first CQD layer 230 has a front side 230F (also referred to as a front surface) and a backside 230B (also referred to as a back surface) opposite the front side 230F. In one or more embodiments, the first CQD layer 230 is deposited on the frontside 220F of the release layer 220 such that the backside 230B of the first CQD layer 230 contacts the front side 220F of the release layer 220.

[0030] Any suitable process may be used to form the first CQD layer 230 on the front side 220F of the release layer 220. In some embodiments, which can be combined with other embodiments herein, the first CQD layer 230 may be deposited by deposition techniques, for example, chemical vapor deposition (CVD), atomic layer deposition (ALD), physical vapor deposition (PVD), thermal evaporation, or sputtering. In some embodiments, which can be combined with other embodiments herein, the first CQD layer 230 may be deposited under vacuum. The first CQD layer 230 may be deposited under vacuum in a roll-to-roll deposition system.

[0031] In one or more embodiments, the first CQD layer 230 can be or include materials such as carbon black, graphite, amorphous carbon, carbon nanotubes, and the like.

[0032] In one or more embodiments, which can be combined with other embodiments herein, the first CQD layer 230 has a thickness in a range from about 1 nanometer to about 5 nanometers, or in a range from about 1 nanometer to about 10 nanometers, or in a range from about 10 nanometers to about 20 nanometers, or in a range from about 20 nanometers to about 50 nanometers.

[0033] Referring to FIG. 2D, at operation 140, a lithium containing layer, such as a lithium metal layer 240 is formed over the front side 230F of the first CQD layer 230. The lithium metal layer 240 includes a front side 240F (also referred to as a front surface) and a backside 250B (also referred to as a back surface) opposite the front side 240F. In one or more embodiments, the lithium metal layer 240 is deposited on the front side 230F of the first CQD layer 230 such that the backside 240B of the lithium metal layer 240 contacts the front side 230F of the first CQD layer 230. The lithium metal layer 240 may be deposited under vacuum. The lithium metal layer 240 may be deposited under vacuum in a roll-to-roll deposition system. The lithium metal layer 240 may be deposited via a physical vapor deposition process,for example, an evaporation process or a sputtering process. The evaporation process may be an electron beam evaporation process or a thermal evaporation process.

[0034] In one or more embodiments, which can be combined with other embodiments described herein, the lithium metal layer 240 has a thickness in a range from about 1 micron to about 100 microns, such as in a range from about 1 micron to about 20 microns, or in a range from about 25 microns to about 50 microns.

[0035] Referring to FIG. 2E, at operation 150, a second carbon quantum dot (CQD) layer 250 is formed over the lithium metal layer 240. The second CQD layer 250 has a front side 250F (also referred to as a front surface) and a backside 250B (also referred to as a back surface) opposite the front side 250F. In one or more embodiments, the second CQD layer 250 is deposited on the front side 240F of the lithium metal layer 240 such that the backside 250B of second CQD layer 250 contacts the front side 240F of the lithium metal layer 240.

[0036] In one or more embodiments, the second CQD layer 250 can be or include materials such as black carbon, graphite, amorphous carbon, carbon nanotubes, and the like. In one embodiment, the second CQD layer 250 is made from the same material as the first CQD layer 230. In other embodiments, the first and second CQD layers 230, 250 are made from different materials.

[0037] In one or more embodiments, which can be combined with other embodiments herein, the second CQD layer 250 has a thickness in a range from about 1 nanometer to about 5 nanometers, or in a range from about 1 nanometer to about 10 nanometers, or in a range from about 10 nanometers to about 20 nanometers, or in a range from about 20 nanometers to about 50 nanometers.

[0038] In some embodiments, the CQDs of the second CQD layer 250 may have surface functional groups that can aid in passivation of lithiummetal anodes / lithium metal anode layers (e.g., the lithium metal layer 240) thereby enhancing electrochemical stability. When directly disposed on the lithium metal layer 240, the second CQD layer 250 can serve as a protective layer for the lithium metal layer 240. For example, the CQDs can protect the lithium metal anode from oxidation and damage during storage and shipping. The CQDs can also inhibit the formation of unwanted solid-electrolyte interphase (SEI) layers on the surface of the lithium metal anode layer, thereby reducing side reactions and enhancing stability during lithium deposition and stripping processes.

[0039] Advantages of such CQD-coated lithium metal anodes can therefore exhibit improved Coulombic efficiency, reduced polarization, and enhanced cycling stability. Advantages for use of the second CQD layer 250 as a passivation layer on lithium metal anodes therefore include preventing the formation of unwanted SEI layers, maintaining high lithium-ion conductivity, and minimizing capacity loss over repeated charge-discharge cycles.

[0040] When in contact with the lithium metal layer 240, the CQDs of the first and second CQD layers 230, 250, may scatter enough light to make the lithium metal layer 240 appear a certain color corresponding to the color of the CQDs. In some embodiments, the color of the CQDs can vary depending on the size (e.g., diameter) of the CQDs used for the first and second CQD layers 230, 250. In some embodiments, CQDs with smaller diameters, for example, between about 2 nanometers and about 3 nanometers can appear blue. CQDs with larger diameters, for example between about 3 nanometers and about 5 nanometers can appear green. CQDs with even larger diameters, such as between about 5 nanometers and about 7 nanometers can appear yellow, orange, or yellowish orange. CQDs with diameters between about 7 nanometers and about 10 nanometers, or larger, can appear red. In some embodiments, the color of the appearance of the lithium metal layer 240 may therefore assist in or be used as an inherent identification method of the first and second CQD layers 230, 250 deposited thereon. The color ranges provided herein are approximate and can varydepending on the specific synthesis methods, surface modifications, and quantum confinement effects present in the CQDs. Additionally, the colors observed may also be influenced by the presence of functional groups, doping elements, or the surrounding environment.

[0041] In some embodiments, the CQDs of the first and second CQD layers 230, 250 may appear transparent. The transparency of the CQD layers can depend on their optical properties. Transparent CQDs typically refer to those that do not significantly absorb or scatter visible light, allowing light to pass through with minimal interference or coloration. The transparency of the CQDs can therefore depend on the size, crystallinity, surface passivation, and bandgap of the CQDs. Generally, smaller CQDs tend to be more transparent as they possess a larger bandgap, which results in a reduced absorption of visible light. The transparency of CQDs can also be affected by other factors such as the concentration of CQDs in a solution or film, as well as the presence of any surface modifications or ligands.

[0042] In one or more embodiments, the lithium metal layer 240 disposed between the first CQD layer 230 and the second CQD layer 250 may be part of a SIDT film stack 255. Referring to FIG. 2E, although the SIDT film stack 255 is shown as including only the lithium metal layer 240 and the first and second CQD layers 230, 250, the SIDT film stack 255 may include additional layers, for example, protective layers, interface layers, and solid electrolyte interface (SEI) layers, among others.

[0043] In one or more implementations, which can be combined with other implementations, an interface layer can optionally be included in the SIDT film stack 255. The interface layers include at least one of an interface dielectric material, plating and stripping enhancement layers, and lithiophilic layers. The interface layers are deposited under vacuum. The interface layers may be deposited under vacuum in a roll-to-roll deposition system. The interface dielectric layer may be selected from AIOx, AIOOH, LiF, BaTiO3, ZrO2, TiO2, Li4Ti5O12, LiAIO2, AIF3, BiF3, AgFx, rare earth (RE) nickelates RENiO3, or a combination thereof. RE can be a trivalent rare- earth. RE can be lanthanide. RE can be selected from La, Pr, Nd, Sm, Eu,Gd, Dy, Ho, Er, Y, Lu, or a combination thereof. The plating and stripping enhancement layers may be selected from metals, alloys of metals, or chalcogenides of the metals. The plating and stripping enhancement layers may be selected from Ag, Bi, Sn, Si, Ga, In, alloys of metals or chalcogenides of Ag, Bi, Sn, Si, Ga, In, or a combination thereof.

[0044] Referring to FIG. 2F, at operation 160, the SIDT film stack 255 is transferred from the flexible support layer 210 to a receiving substrate 260 to form an anode device stack 265. Operation 160 may include lamination transfer of the SIDT film stack 255 onto the receiving substrate 260 to form the anode device stack 265. The receiving substrate 260 may be or include flexible film, such as a CPP film (i.e. , a casting polypropylene film), an OPP film (i.e., an oriented polypropylene film), or a PET film (i.e., a polyethylene terephthalate film). Alternatively, the receiving substrate 260 may be a precoated paper, a polypropylene (PP) film, a PEN film, a polylactic acid (PLA) film, or a PVC film. The receiving substrate 260 can include one or more layers. The receiving substrate 260 can be or include one or more current collectors. For example, the current collector can include aluminum (Al), copper (Cu), zinc (Zn), nickel (Ni), cobalt (Co), manganese (Mn), chromium (Cr), stainless steel, clad materials, alloys thereof, and a combination thereof. In various embodiments, the receiving substrate 260 can be or includes copper or copper foil. In one or more embodiments, which can be combined with other embodiments described herein, the receiving substrate 260 includes a web-based substrate, for example, the current collector can be a web-based substrate.

[0045] As shown in FIG. 2F, the anode device stack 265 includes the second CQD layer 250 disposed between the lithium metal layer 240 and the receiving substrate 260. In some embodiments, the receiving substrate 260 may be an anode current collector comprising copper or copper foil. In such embodiments, the CQDs of the second CQD layer 250 form a conformal interface on the receiving substrate 260 and can serve as a conductive interface between the lithium metal layer 240 and the current collector (e.g., the receiving substrate 260). The conductive nature of the CQDs of thesecond CQD layer 250 enables the second CQD layer 250 to provide a low- resistance pathway for electron transport for facilitating efficient electron transfer between the lithium metal layer 240 and the receiving substrate 260. Advantages of use of the CQDs as a coating component on the lithium metal anode may therefore include minimizing energy losses and enhancing overall battery performance.

[0046] In one or more embodiments, which can be combined with other embodiments, during operation 160 the release layer 220 is transferred or partially transferred with the SIDT film stack 255 as is shown in FIG. 2F. Alternatively, in other embodiments, the release layer 220 remains or partially remains on the flexible support layer 210 after operation 160.

[0047] Optionally, at operation 160, pressure (not shown) may be applied to one or more of the receiving substrate 260 and the flexible support layer 210 having the SIDT stack 255 formed thereon to laminate the receiving substrate 260 to the second CQD layer 250. In some embodiments, where the method 100 is performed in a roll-to-roll tool, web tension is sufficient to laminate the second CQD layer 250 to the receiving substrate 260 and additional pressure is not needed. In some implementations, where additional pressure is used to laminate the second CQD layer 250 to the receiving substrate 260, the lamination process includes pressing the second CQD layer 250 to the receiving substrate 260 with a magnitude of pressure sufficient to attach the second CQD layer 250 to the receiving substrate 260 without damaging the SIDT stack 255. In other words, the pressure is such that each of the layers of the SIDT stack 255 is not mechanically destroyed or degraded, such as by cracking or crushing. Pressure may be applied using any suitable techniques. In one or more embodiments, pressure is applied via a calendering process. The calendering process may include using a pair of calendering rollers if the method 100 is performed in a roll-to- roll web coating system. For example, pressure may be applied to the backside 210B of the flexible support layer 210 and a backside of the receiving substrate 260. In one or more other embodiments, pressure isapplied by a vacuum source. In one or more other implementations, the pressure is external pressure.

[0048] Referring to FIG. 2G, at optional operation 170, the anode device stack 265 may be combined with a separator 290, a cathode stack 285, or both the separator 290 and the cathode stack 285 to form the energy storage device structure 200. In some embodiments, the energy storage device structure 200, even though shown as a planar structure in FIG. 2G, may also be formed into a cylinder by rolling the stack of layers; furthermore, other cell configurations (e.g., prismatic cells, button cells, or stacked electrode cells) may be formed.

[0049] The separator 290 may include a microporous polymeric separator including a polyolefin, by way of a non-limiting example. The polyolefin may be a homopolymer (derived from a single monomer constituent) or a heteropolymer (derived from more than one monomer constituent), which may be either linear or branched. If a heteropolymer is derived from two monomer constituents, the polyolefin may assume any copolymer chain arrangement, including those of a block copolymer or a random copolymer. Similarly, if the polyolefin is a heteropolymer derived from more than two monomer constituents, it may likewise be a block copolymer or a random copolymer. In certain embodiments, the polyolefin may be polyethylene (PE), polypropylene (PP), or a blend of PE and PR, or multi-layered structured porous films of PE and / or PP. Commercially available polyolefin porous membranes include CELGARD® 2500 (a monolayer polypropylene separator) and CELGARD® 2320 (a tri-layer polypropylene / polyethylene / polypropylene separator) available from Celgard LLC.

[0050] In one or more embodiments, which can be combined with other embodiments, the cathode stack 285 includes a cathode current collector 280 and a cathode material layer 270. The cathode current collector 280 may be or include any of the flexible films described and aluminum (Al), copper (Cu), zinc (Zn), nickel (Ni), cobalt (Co), tin (Sn), silicon (Si), manganese (Mn), magnesium (Mg), alloys thereof, and combinationsthereof. The cathode current collector 280 may be or include any of aluminum (Al), copper (Cu), zinc (Zn), nickel (Ni), cobalt (Co), tin (Sn), silicon (Si), manganese (Mn), magnesium (Mg), alloys thereof, and combinations thereof. In various embodiments, the cathode current collector 280 may be or include aluminum.

[0051] The cathode material layer 270 may be or include any suitable cathode material. The cathode material layer 270 or cathode may be or include any material compatible with the anode and may include an intercalation compound, an insertion compound, or an electrochemically active polymer. Suitable intercalation materials include, for example, sulfur, lithium-containing metal oxides, M0S2, FeS2, MnO2, TiS2, NbSes, LiCoCte, LiNiC>2, LiMnO2, LiMn2O4, VeOn and V2O5. Suitable polymers include, for example, polyacetylene, polypyrrole, polyaniline, and polythiophene. In some embodiments, the cathode material layer 270 includes a polymer binder material as described herein. The cathode material layer 270 or cathode may be or include a layered oxide, such as lithium cobalt oxide, an olivine, such as lithium iron phosphate, or a spinel, such as lithium manganese oxide. Examples of lithium-containing oxides may be layered, such as lithium cobalt oxide (LiCoCte), or mixed metal oxides, such as LiNixCoi-2xMnO2, LiNiMnCoO2(“NMC”), LiNio.5Mm.5O4, Li(Nio.8Coo.i5Alo.o5)02, LiMn2O4, and doped lithium rich layered-layered materials, wherein x is zero or a non-zero number. Examples of phosphates may be or include iron olivine (LiFePO4) and it is variants (such as LiFe(i- x)MgxPO4), LiMoPO4, LiCoPO4, LiNiPCU, Li3V2(PO4)3, LiVOPO4, UMP2O7, or LiFei.sP2O7, wherein x is zero or a non-zero number. Examples of fluorophosphates may be or include LiVPO4F, LiAIPCUF, LisV(PO4)2F2 LisCr(PO4)2F2 Li2CoPO4F, or Li2NiPO4F. Example of silicates may be or include Li2FeSiO4, Li2MnSiO4, or Li2VOSiO4. Examples of non-lithium compounds may be or include NasV2(PO4)2F3.

[0052] In some embodiments, an anode material may already be formed over the receiving substrate 260. In such embodiments, the SIDT film stack 255 may be transferred to contact the second CQD layer 250 with the anodematerial formed over the receiving substrate 260 and pre-lithiate the anode material already formed over the receiving substrate 260. The already formed anode material can include or be, but is not limited to, graphite, silicon, silicon graphite, silicon oxide graphite, silicon, metalized plastic, and copper.

[0053] The anode device stack 265 described herein is formed such that the lithium metal layer 240 is disposed between layers of carbon quantum dots. As discussed herein, the layers of CQDs can protect the lithium metal layer 240 from moisture and oxidation, thereby improving the stability of the lithium metal anode as well as the safety when handling and transporting such anode device stacks during the Li-ion battery fabrication process. As applied to roll-to-rol I manufacturing of the anode device stack 265, the layers of CQDs can improve safety when handling, transporting, and storing the rolls of the anode device stack 265, as well as preserve and maintain the functionality of the lithium of the lithium metal layer 240.

[0054] FIG. 3 illustrates a cross-sectional view of an anode electrode structure 300, according to certain embodiments of the present disclosure. Although the anode electrode structure 300 is depicted as a dual-sided electrode structure, it should be understood that the implementations described herein also apply to single-sided electrode structures.

[0055] In an embodiment, the CQDs can be used as a protective coating on the lithium metal anode. As shown in FIG. 3, the anode electrode structure 300 has a an anode current collector 302 and anode material layers 304a, 304b (collectively 304) formed on opposing sides of the anode current collector 302. Examples of metals that the current collector 302 may be comprised of aluminum (Al), copper (Cu), zinc (Zn), nickel (Ni), cobalt (Co), manganese (Mn), chromium (Cr), stainless steel, clad materials, alloys thereof, and a combination thereof. In one embodiment, the anode material layers 304 are lithium metal layers. In one embodiment, each of the anode material layer 304 has a thickness of about 100 microns or less (e.g., from about 1 microns to about 100 microns). A CQD layer 306a, 306b (collectively306) is formed on each of the anode material layers 304a, 304b to coat the resulting anode electrode structure 300.

[0056] In an embodiment, which can be combined with other embodiments described herein, the anode electrode structure 300 maybe formed by forming the anode material layer 304 on a substrate, such as the anode current collector 302. In one embodiment, the anode material layer 304 is a lithium metal layer. In some embodiments, if an anode film is already present on the substrate, the lithium metal layer is formed on the anode material layer 304. If the anode material layer 304 is not present, the lithium metal layer may be formed directly on the substrate. Any suitable lithium metal film deposition process for depositing thin films of lithium metal may be used to deposit the thin film of lithium metal. Deposition of the thin film of lithium metal may be by PVD processes, such as evaporation (e.g., thermal evaporation or e-beam), a slot-die process, a transfer process, or a three- dimensional lithium printing process. The chamber for depositing the thin film of lithium metal may include a PVD system, such as an electron-beam evaporator, a thermal evaporator, or a sputtering system, a thin film transfer system (including large area pattern printing systems such as gravure printing systems) or a slot-die deposition system.

[0057] After the anode material layer 304 is formed, the CQD layers 306 is formed on the anode material layer 304. In some embodiments, the CQD layers 306 have a thickness in a range of about 1 nanometer to about 5 nanometers, or in a range of about 1 nanometer to about 10 nanometers, or in a range of about 10 nanometers to about 20 nanometers, or in a range of about 20 nanometers to about 50 nanometers. In some embodiments, the CQD layers 306 can be formed on the anode material layer 304 using any of the deposition techniques described herein for depositing CQD layers, for example, chemical vapor deposition (CVD), atomic layer deposition (ALD), physical vapor deposition (PVD), thermal evaporation, or sputtering.

[0058] The coating by the CQD layers 306 can advantageously improve the performance of the anode. For example, the CQD layer can increasing the conductivity of the anode by providing more pathways for electrons toflow. This can lead to a significant improvement in the performance of the anode, especially at high discharge rates. The CQD layer can also reduce the surface area of the anode by filling in the pores and crevices on the surface of the anode. This can help to prevent the formation of lithium dendrites, which can cause short circuits and safety hazards. The CQD can also improve the stability of the anode by providing a protective barrier against oxidation and corrosion. This can help to extend the lifespan of the anode and improve its performance over time.

[0059] As applied to the resulting Li-ion battery manufactured using the anode device stack 265, the layers of CQDs can improve the electrochemical performance of the battery due to decreased resistance or impedance now associated with the anode of the battery. The layers of CQDs can also increase the conductivity of the lithium metal anode by providing more pathways for electrons to flow between the lithium metal layer and the current collector layer of the anode.

[0060] In addition to protecting the lithium from oxidation and moisture, the CQDs can also improve safety by decreasing the risk of battery damage caused by welling of the anode during use. Specifically, the CQDs can assist in reducing the volume change exhibited by lithium during lithiation and delithiation of the battery which can cause stress and strain on the anode. The CQDs can reduce the extent of the volume change of the anode by providing a more uniform distribution of lithium ion, thereby improving the lifespan and potentially the performance of the anode over time.

[0061] Another benefit provided by the CQDs implemented with the lithium containing layers includes providing a greater resistance to dendrites, or the sharp, uneven build-up of lithium that forms during movement from the cathode to the anode. Lithium dendrites are known to cause short circuits and pose as safety hazards if such dendrites form and in extreme cases, pierce the separator between the cathode and anode. In another aspect, the layers of CQDs can reduce the surface area of the lithium metal anode by filling in the pores and crevices on the surface of the anode, thereby reducing the risks associated with the formation of lithium dendrites.

[0062] Embodiments described may be performed in a roll-to-roll coating system, such as a TopMet® roll-to-roll web coating system, a SMARTWEB® roll-to-roll web coating system, a TOPBEAM® roll-to-roll web coating system, all of which are available from Applied Materials, Inc. of Santa Clara, California. Other tools capable of performing high rate deposition processes may also be adapted to benefit from the embodiments described herein. In addition, any system enabling the deposition processes described herein can be used to advantage. It should also be understood that although described as a roll-to-roll process, the embodiments described may also be performed on discrete substrates.

[0063] While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

Claims

What is claimed is:1 . A method for forming a device stack, comprising: forming a first carbon quantum dot layer over a release layer disposed over a flexible support layer; depositing a lithium metal layer on the first carbon quantum dot layer; forming a second carbon quantum dot layer over the lithium metal layer; and transferring the first carbon quantum dot layer, the lithium metal layer, and the second carbon quantum dot layer to a receiving substrate.

2. The method of claim 1 , wherein each of the first and second carbon quantum dot layers comprises a material selected from the group consisting of carbon black, graphite, amorphous carbon, carbon nanotubes, and the like.

3. The method of claim 1 , wherein each of the first and second carbon quantum dot layers comprises a thickness in a range from about 1 nanometer to about 10 nanometers, or in a range from about 10 nanometers to about 20 nanometers, or in a range from about 20 nanometers to about 50 nanometers.

4. The method of claim 1 , wherein each of the first and second carbon quantum dot layers is formed by a chemical vapor deposition (CVD) process, an atomic layer deposition (ALD) process, a physical vapor deposition (PVD) process, a thermal evaporation process, or a sputtering process.

5. The method of claim 1 , wherein the flexible support layer comprises a material selected from the group consisting of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyimide (PI), poly(methyl methacrylate) (PMMA), cellulose tri-acetate (TAC), polypropylene (PP), polyethylene (PE), polycarbonates (PC), multilayers thereof, or a combination thereof.

6. The method of claim 1 , wherein the receiving substrate comprises a current collector.

7. The method of claim 1 , wherein the receiving substrate comprises an anode material layer formed on a current collector.

8. The method of claim 1 , wherein the receiving substrate comprises copper.

9. The method of claim 1 , wherein the lithium metal layer is deposited on the first quantum dot layer by a physical vapor deposition process, an evaporation process or a sputtering process.

10. The method of claim 1 , wherein the second carbon quantum dot layer formed over the lithium metal layer provides a passivation layer over the lithium metal layer.

11. A lithium metal anode device stack, comprising: a current collector; a lithium metal layer formed on the current collector; and a carbon quantum dot layer formed on the lithium metal layer, the carbon quantum dot layer comprising a material selected from the group consisting of carbon black, graphite, amorphous carbon, carbon nanotubes, and the like.

12. The lithium metal anode device stack of claim 11 , wherein the carbon quantum dot layer comprises a thickness in range from about 1 nanometer to about 10 nanometers, from about 10 nanometers to about 20 nanometers, or from about 20 nanometers to about 50 nanometers.

13. A lithium metal anode device stack, comprising: a current collector; a first carbon quantum dot layer and a second carbon quantum dot layer disposed on the current collector; and a lithium metal layer disposed between the first and second carbon quantum dot layers.

14. The lithium metal anode device stack of claim 13, wherein each of the first and second carbon quantum dot layers comprises a material selected from the group consisting of carbon black, graphite, amorphous carbon, carbon nanotubes, and the like.

15. The lithium metal anode device stack of claim 1113 wherein each of the first and second carbon quantum dot layers comprises a thickness in range from about 1 nanometer to about 10 nanometers, from about 10 nanometers to about 20 nanometers, or from about 20 nanometers to about 50 nanometers.

16. The lithium metal anode device stack of claim 13, further comprising an anode material layer disposed between the current collector and the first carbon quantum dot layer.

17. The lithium metal anode device stack of claim 13, wherein the first carbon quantum dot layer aids in preventing the formation of dendrites between the lithium metal layer and a separator of a cathode stack.

18. The lithium metal anode device stack of claim 11 , wherein the current collector comprises copper or copper foil.

19. The lithium metal anode device stack of claim 11 , wherein the first and second carbon quantum dot layers cause the lithium metal layer to appear blue, green, yellow, orange, yellowish orange, or red.

20. The lithium metal anode device stack of claim 11 , wherein the second carbon quantum dot layer disposed between the current collector and the lithium metal layer forms a conductive interface for facilitating electron transfer between the current collector and the lithium metal layer.

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